Sub-grade structures, or vaults, as the term is alternatively used herein, are open-topped structures with an internal cavity. It is common practice for such vaults to be placed where persons can be expected to walk, or where vehicles are to travel. They are used for a multitude of purposes, among them being terminal boxes for electrical cables, communication cables, collectors for drainage of surface water such as caused by draining basins, area drainage collectors for storm water sewer system, surface receptacles for hoses, and manhole and equipment entry ports for any of these.
It is common practice to place a cover on the top of the vault to close it. The cover is intended to protect a person or vehicle from falling into the it at the risk of physical injury from a fall, or exposure to electrical hazard, and to protect the contents of the vault from theft or vandalism. Absence of the cover exposes the person, vehicle, and vault contents to such risks.
One could reasonably expect that a pedestrian or driver would look to see where they are stepping or driving and should notice the relatively large hole that exists when the cover is missing, and avoid it. The realities of litigation suggest that this expectation should not be relied on, but rather that pro-active efforts be made to provide a visual warning that the cover is missing.
Also, such a warning could usefully be transmitted to a supervisory system that can alert the operator to the absence of the cover, and more importantly, to the existence of a vault with its top open and its contents exposed.
It is an object of this invention to provide a passive device which is out of sight and restrained when a cover is properly in place, but which, when the cover is open or missing, will by its own mechanically stored energy immediately rise to provide an above ground visible indicia adjacent to, above, and perhaps also over the opening, so as to alert persons to the fact of an open vault. It can be held down and out of sight only by a cover properly in place on the top of the vault.